Dennis Ross, just retired as President Barack Obama’s top adviser on the Middle East, warned yesterday that Obama means what he says when he declares that the White House isn’t ruling out military action against Tehran. Though other, senior U.S. officials, including Defense Secretary Leon Panetta and Adm. Mike Mullen, former chairman of the Joint Chiefs of Staff, have repeatedly stressed that war against Iran could have unpredictable and dangerous results, Ross said Obama is serious about using force to prevent Iran from acquiring a military nuclear capability.

“He hasn’t been reluctant to use force when he says that all options remain on the table,” said Ross, in an appearance at the Washington Institute for Near East Policy (WINEP). “It means that it’s an option he is prepared to exercise.” Later, in a private discussion, Ross told The Diplomat that even though Panetta, Mullen and others in the administration seem to oppose a strike against Iran, “The president doesn’t take his own words lightly. Has he made a decision yet? No.”

Ross, before going into the administration in 2009, spent many years at the Washington Institute, a hawkish, pro-Israel think tank, and he has returned there as its counselor and resident expert on the region. While at the White House, he had a reputation as a hardliner on Iran policy, and there has been speculation in Washington that he left the White House because of differences with other U.S. officials, including Pentagon leaders who have expressed reluctance to attack Iran even if that appears to be the only way to halt Iran’s nuclear research program. But in his WINEP appearance Tuesday, Ross disputed that, saying instead that he quit after three years in order to keep a promise he’d made to his family.

Though Iran has denied that it seeks to militarize its nuclear program, and despite there being no concrete evidence that Iranian leaders have decided to seek nuclear weapons, Ross said in his view there’s no ambiguity. “The Iranians, by their behavior, have made it pretty clear that they want to have a nuclear weapons program,” he said. He emphasized that the goal of U.S. policy is to prevent Iran from building a bomb, not containing it once it has developed a military nuclear capability. “It’s not about containment, it’s about prevention,” he said.

Because neither sanctions nor diplomacy have dissuaded Iran from its nuclear program, many analysts in Washington have begun to talk about containing a nuclear Iran, much as the United States pursued a containment, balance-of-power policy toward the Soviet Union in the Cold War. And it’s been reported that officials at the White House, the State Department and the Defense Department are quietly discussing precisely that idea if Iran eventually decides to go nuclear.

But Ross laid out an apocalyptic scenario for nuclear Armageddon in the Middle East if Iran gets the bomb. Were Iran to acquire even a limited nuclear capability, it would dramatically destabilize the Middle East, he said, and that’s why a containment policy is the wrong approach. “The fact is that Israel looks at Iran as an existential threat, and it is,” he said. If both Israel and Iran have nuclear bombs, it would put the region on a hair trigger, and he asked, “Can Israel wait?” if a nuclear-armed Iran seemed to raise its level of readiness for war. “The possibility of nuclear war in the Middle East goes up dramatically.”

Ross stressed that there’s still room for the administration’s combination of sanctions and negotiation to work. “We still have time and space available to us to ratchet up the pressure,” he told WINEP. But some analysts have argued that sanctions, pressure tactics and what appears to be a campaign of covert action against Iran could provoke Iran into aggressive, rash behavior that could by itself lead to conflict. In the field of covert action, recent events include the assassination of several Iranian scientists, a computer worm that damaged Iran’s centrifuge facility, an explosion that killed the top Iranian commander in charge of its missile program, and the recent crash of a U.S. surveillance drone in eastern Iran. Ross refused to comment on whether or not the United States has a covert action program underway, but when asked about it he replied cryptically, “The full range of options needs to be pursued. All options need to be explored.”

One argument against war with Iran, and against harsh economic sanctions that would include curtailing or cutting off Iran’s oil exports, is that the loss of Iran’s oil on the world market would send prices skyrocketing. But Ross suggested that quiet talks with Saudi Arabia, the United Arab Emirates, and Kuwait – all of which have expressed alarm about Iranian ambitions in the Gulf – might lead Arab oil producers to ratchet up their output to offset Iranian exports. And, he said, Libya’s oil output is already coming back onto the market, further easing pressure on prices. Thus, he said, it might be possible to “phase in an Iran oil shutoff without a spike in prices.”